U.S. patent number 4,459,516 [Application Number 06/392,004] was granted by the patent office on 1984-07-10 for line operated fluorescent lamp inverter ballast.
Invention is credited to Francis J. Zelina, William B. Zelina.
United States Patent |
4,459,516 |
Zelina , et al. |
July 10, 1984 |
Line operated fluorescent lamp inverter ballast
Abstract
Applicant has provided a ballast circuit for fluorescent lights
made up of the combination of (1) a source of electrical energy,
(2) a resonant circuit, (3) a switch means for connecting the
source of electricity to the resonant circuit, (4) means to connect
the resonant circuit to a load, (5) a resonant current monitor
controlling the switch means in synchronism with the resonant
current so that the switch means switches the resonant current when
the resonant current passes through zero. The resonant current
monitor is a current transformer having a primary winding connected
in series with the resonant circuit and two secondary windings
connected to the bases of the two switching transistors in a two
transistor inverter circuit at a polarity that will switch one of
the transistors on and the other off at the time current passes
through zero. This is the optimum time to switch the transistors
since the current flowing through the transistors is passing
through zero at that time and therefore the transistors operate at
maximum efficiency and there are minimum switching losses and
improves the efficiency of the circuit. The circuit will
automatically adjust the switching frequency to the changed
resonant frequency should the value of the inductor or the
capacitor degrade and therefore change, and the switching losses
will therefore be maintained at minimum.
Inventors: |
Zelina; William B. (Erie,
PA), Zelina; Francis J. (Erie, PA) |
Family
ID: |
26960577 |
Appl.
No.: |
06/392,004 |
Filed: |
June 25, 1982 |
Related U.S. Patent Documents
|
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
|
280866 |
Jul 6, 1981 |
|
|
|
|
Current U.S.
Class: |
315/209R;
315/219; 315/244; 315/223; 315/276 |
Current CPC
Class: |
H05B
41/295 (20130101); H05B 41/2825 (20130101); H05B
41/232 (20130101) |
Current International
Class: |
H05B
41/28 (20060101); H05B 41/282 (20060101); H05B
41/232 (20060101); H05B 41/295 (20060101); H05B
41/20 (20060101); H05B 037/02 () |
Field of
Search: |
;331/113A
;315/DIG.7,219,209,219,223,244,276,DIG.7 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Dixon; Harold
Attorney, Agent or Firm: Lovercheck; Charles L. Lovercheck;
Wayne L. Lovercheck; Dale R.
Parent Case Text
REFERENCE TO PRIOR APPLICATIONS
This Application is a continuation in part of Pat. application Ser.
No. 280,866 filed July 6, 1981 now abandoned.
Claims
We claim:
1. A circuit for driving a load comprising,
a resonant circuit,
a power supply,
an inverter circuit,
control means for actuating said inverter,
a first transformer having a winding,
a second transformer having a primary winding, a first secondary
winding and a second secondary winding, said primary winding having
a few turns only,
a condenser,
a first electronic valve having an actuating means,
a second electronic valve having an actuating means,
said resonant circuit comprising said first transformer winding,
said second transformer primary winding and said condenser
connected in series with one another and adapted to carry resonant
circuit current, said second transformer being a current
transformer,
said inverter comprising said first electronic valve and said
second electronic valve,
said first electronic valve being connected to said power supply
and to said resonant circuit,
said second electronic valve being connected in series with said
resonant circuit forming a loop,
said first secondary winding of said second transformer being
connected to said actuating means on said first electronic
valve,
said second secondary winding of said second transformer being
connected to said actuating means of said second electronic
valve,
said control means for actuating said inverter consisting of said
second transformer,
said second transformer first secondary being adapted to actuate
said first electronic valve connecting said power supply to said
resonant circuit to charge said condenser to a first polarity,
said second transformer second secondary winding being adapted to
actuate said second electronic valve connecting said resonant
circuit into a loop allowing current to flow in said loop to charge
said condenser to a second polarity,
and means on said circuit for connecting said first transformer
winding to a load.
2. The circuit recited in claim 1 wherein said second transformer
is a current transformer.
3. The circuit recited in claim 1 wherein said first transformer
winding is primary winding and said means connecting said circuit
to a load comprises a secondary winding on said first
transformer.
4. The inverter circuit recited in claim 1 wherein said first
transformer has a second secondary winding and a third secondary
winding and said load means comprises a fluorescent lamp connected
to said first secondary winding of said first transformer and
having a first heater and a second heater,
said second secondary transformer winding of said first transformer
being connected to said first heater means and said third
transformer winding of said first transformer being connected to
said second heater means on said fluorescent lamp,
said voltage in said secondary windings being adapted to reduce to
a substantially low value during the time that the gas in said
fluorescent lamp is ionized.
5. The circuit recited in claim 1 wherein said load is an ionizable
gas lamp.
6. The circuit recited in claim 1 wherein said load is a
fluorescent lamp.
7. The circuit recited in claim 5 wherein said fluorescent lamp has
heating elements,
said second winding is connected to said heating means.
8. A circuit for driving a load comprising,
a resonant circuit,
a power supply,
an inverter circuit,
control means for actuating said inverter,
a first transformer having a winding,
a second transformer having a primary winding, a first secondary
winding and a second secondary winding,
a condenser,
a first electronic valve having an actuating means,
a second electronic valve having an actuating means,
said resonant circuit comprising said first transformer winding,
said second transformer primary winding and said condenser
connected in series with one another and adapted to carry resonant
circuit current,
said inverter comprising said first electronic valve and said
second electronic valve,
said first electronic valve being connected to said power supply
and to said resonant circuit,
said second electronic valve being connected in series with said
resonant circuit forming a loop,
said first secondary winding of said second transformer being
connected to said actuating means on said first electronic
valve,
said second secondary winding of said second transformer being
connected to said actuating means on said second electronic
valve,
said control means for actuating said inverter consisting of said
second transformer,
said second transformer first secondary being adapted to actuate
said first electronic valve connecting said power supply to said
resonant circuit to charge said condenser to a first polarity,
said second transformer second secondary winding being adapted to
actuate said second electronic valve connecting said resonant
circuit into a loop allowing current to flow in said loop to charge
said condenser to a second polarity,
and means on said circuit for connecting it to a load,
said load is a fluorescent lamp,
said fluorescent lamp has heating elements,
said second winding is connected to said heating means,
said first transformer is a high leakage reactance transformer
magnetically coupled to said secondary winding.
9. The circuit recited in claim 8 wherein said first transformer
comprises a magnetic core in the form of a magnetic structure.
10. The circuit recited in claim 9 wherein said second transformer
has a core made of a material having the magnetic properties of
ferrite.
11. A circuit for driving a load comprising,
a resonant circuit,
a power supply,
an inverter circuit,
control means for actuating said inverter,
a first transformer having a winding,
a second transformer having a primary winding, a first secondary
winding and a second secondary winding,
a condenser,
a first electronic valve having an actuating means,
a second electronic valve having an actuating means,
said resonant circuit comprising said first transformer winding,
said second transformer primary winding and said condenser
connected in series with one another,
said inverter comprising said first electronic valve and said
second electronic valve,
said first electronic valve being connected to said power supply
and to said resonant circuit,
said second electronic valve being connected in series with said
resonant circuit forming a loop,
said first secondary winding of said second transformer being
connected to said actuating means on said first electronic
valve,
said second secondary winding of said second transformer being
connected to said actuating means of said second electronic
valve,
said control means for actuating said inverter consisting of said
second transformer,
said second transformer first secondary being adapted to actuate
said first electronic valve connecting said power supply to said
resonant circuit to charge said condenser to a first polarity,
said second transformer second secondary winding being adapted to
actuate said second electronic valve connecting said resonant
circuit into a loop allowing current to flow in said loop to charge
said condenser to a second polarity,
and means on said circuit for connecting it to a load,
said second transformer is a current transformer having an annular
core made of a material having the properties of ferrite.
12. The circuit recited in claim 11 wherein second transformer has
a core made of an annular member.
13. The circuit recited in claim 12 wherein said annular member has
an opening there through and said windings wound on said annular
member through said opening.
14. A circuit for driving a load comprising,
a resonant circuit,
a power supply,
an inverter circuit,
control means for actuating said inverter,
a first transformer having a winding,
a second transformer having a primary winding, a first secondary
winding and a second secondary winding,
a condenser,
a first electronic valve having an actuating means,
a second electronic valve having an actuating means,
said resonant circuit comprising said first transformer winding,
said second transformer primary winding and said condenser
connected in series with one another,
said inverter comprising said first electronic valve and said
second electronic valve,
said first electronic valve being connected to said power supply
and to said resonant circuit,
said second electronic valve being connected in series with said
resonant circuit forming a loop,
said first secondary winding of said second transformer being
connected to said actuating means on said first electronic
valve,
said second secondary winding of said second transformer being
connected to said actuating means of said second electronic
valve,
said control means for actuating said inverter consisting of said
second transformer,
said second transformer first secondary being adapted to actuate
said first electronic valve connecting said power supply to said
resonant circuit to charge said condenser to a first polarity,
said second transformer second secondary winding being adapted to
actuate said second electronic valve connecting said resonant
circuit into a loop allowing current to flow in said loop to charge
said condenser to a second polarity,
said second transformer primary has a single turn.
Description
REFERENCE TO PRIOR ART
The Wenrich Patent discloses a load T2 connected in parallel with
the series-parallel circuit made up of transformer T1 and capacitor
C6. T1 and C6 like any other inductive-capacitance circuit could be
designed to resonate at some frequency, using the familiar equation
##EQU1## however the Wenrich circuit would not function as designed
if it was designed to resonate and such design to resonate could
only be done in view of Applicant's disclosure viewed in retrospect
since Wenrich does not teach resonants but to the contrary teaches
a inductor that will saturate and provide a surge of current which
will trigger the transistors.
The Engel inverter frequency is controlled by the timer made up of
the winding 24a and resistors 26 while Wenrich's circuit operates
off an inductance which saturates and the capacitor limits the
current flow when at the point the circuit saturates so that the
inverter switches when the current through the inductance and
capacitance is maximum. This is exactly the thing that Applicant is
attempting to avoid and is exactly opposite from Applicant's
circuit operation.
Both Wenrich and Engel will switch when the inverter has
substantial current flowing and not as the current passes through
zero. Neither Engel nor Wenrich provide a resonant current monitor
for the resonant circuit current for controlling the switching
means.
U.S. Pat. No. 3,753,076 shows an inverter ballast circuit which
utilizes the energy stored in a resonant circuit to reduce input
current to a value near zero during switching. U.S. Pat. No.
4,023,067 shows an inverter circuit that provides minimum switching
losses by use of resonant storage techniques and a unique feedback
system. It attempts to promote zero current switching. The present
circuit assures zero current switching.
U.S. Pat. Nos. 4,031,454, 4,245,177, 4,279,001 and 3,179,901 show
the state of the art but are not relevant to the claims herein.
BACKGROUND OF THE INVENTION
General
The superior lumen per watt characteristic of fluorescent lamps has
for decades prompted research on ways to operate these lamps from a
DC supply. These applications included the transportation industry
(trains, transit cars, buses and airplanes) and the portable
lighting industry. In these applications, no AC power is available
and therefore the premium cost of these inverter ballasts was
justified since the only alternate light source was the
incandescent lamps (about 15 lumens per watt). When compared with
fluorescent lamps of about 50 lumens per watt and about 10 times
the life, the additional inverter ballast cost was justified.
It has been demonstrated as early as the early 50's, that the
fluorescent lamp, when properly operated at frequencies above 15
KHZ, would demonstrate about 15% improvement in the output lumens
per watt over 60 HZ operation. This well recognized fact, plus the
present impetus on energy saving, has been the driving force behind
multi-million dollar research and development efforts to apply high
frequency lighting to commercial, industrial, and consumer
applications. To date, there has been limited success in this
effort. The reason for this record can be understood by studying
the complexity of the problem added to the economics of the
situation. Many efforts produced costs many times that of the 60 HZ
Ballast counterpart with efficiencies, or ballast losses comparable
or worse than the 60 HZ Ballast. Further, 60 HZ Ballast
manufacturing has generally responded with better steel and more
copper to improve their efficiency.
The Problem
The problem of making High Frequency available for general
fluorescent lighting can be defined in the following
categories:
A. Efficiency - must approach 95%. This makes payback an economic
reality.
B. Cost - The cost of the High Frequency Ballasts must be no more
than 2 or 3 times the cost of the 60 HZ Ballast.
C. Reliability - The inverter ballast must match or better the 60
HZ Ballast.
D. Life - Typical life must exceed ten years.
Many of the above problems are interdependent. For example, 95%
efficient means extremely small losses and therefore low
temperature rise, which generally means high reliability and long
life. However, generally, cost tends to increase when the above
objectives are addressed. We can then summarize our problem
statement by saying the following: We must find a solution, if one
exists, that will demonstrate the high efficiency and low loss with
primary effort on production simplicity and low costs.
Solution to Problem
It has been generally accepted by these inventors since their first
lighting of a fluorescent lamp with an inverter ballast, in the mid
50's, that resonance plays a dominant factor in ballast efficiency.
However, maintaining resonance with component tolerances in
production and during aging of the ballast appeared to be an
impossible problem. In 1970, during work on the Coleman Camping
Lantern ballast, the inventors were successful in providing
resonant feedback which solved the above problem and produced
efficiencies approaching 90%. This technology is used extensively
in the transit industry and is the basis of Pat. No. 3,753,076.
Following this work, a single transistor resonant feedback ballast
was developed which approached 95% efficiency. This technology is
the basis for most of the low voltage camping lantern ballasts made
today, for example, Pat. No. 4,023,067. The resonant feedback
promotes zero current switching of the transistor thereby providing
the high efficiency.
The teaching contained herein goes an order of magnitude further in
that, instead of promoting zero current switching, it assures it.
Further, the start up transient is addressed in such a manner that
the switching devices are less stressed during start up. Still, the
above solutions have been accomplished in such a manner that a cost
effective solution has been demonstrated. The 25% to 30% overall
energy savings with no change in light output can easily justify
the higher inverter ballast cost. Retrofitting field ballast should
be possible with an approximate one year payback, depending upon
local energy and labor costs.
The operation of the inverter in synchronism with the resonant
current also automatically adjusts the switching frequency to the
resonant frequency should the value of the inductor or capacitor
degrade and therefor change. The switching losses will therefore be
maintained at a minimum.
SUMMARY OF INVENTION
The solution to the problem discussed will be described using FIG.
1 through FIG. 4. Before we start, we should review our knowledge
of simple series resonant circuit operation. It should be recalled
that in a simple series resonant circuit the voltage across the
capacitor will be 180 degrees out of phase with the inductance and
the current flowing will be 90 degrees out of phase with both the
capacitor and inductor voltages ignoring leading and lagging
relationships. With reference to FIG. 1, one skilled in the art can
determine relative relationships of the electrical quantities
without experimentation. Note also that when current I.sub.r
(resonant current) goes through zero, the stored energy in
condenser 22 (C) is a maximum (1/2 CV.sup.2) and the stored energy
in (the reactance 14 and 18) L is at zero (1/2 LI.sup.2).
If we can inject energy into the tank as I.sub.r goes through zero,
11 will switch at zero current and conduct a half sine wave of
current into the LC tank circuit. If, as I.sub.r goes through zero,
we turn 11 off and 12 on, we take the stored energy in Condensor 22
and transfer it in reverse polarity to Condensor 22. In this
fashion, we continue to increase stored energy and voltage (the
same) in the tank circuit. If energy is not removed from the
resonant tank, voltages (energy) will build to component
destruction.
Now, we must address ourselves to a better understanding of gas arc
lamps (fluorescent lamps). Their general characteristic is such
that an arc ionization voltage of about 2 to 3 times the operating
voltage is required. If we couple the fluorescent lamp into the
tank circuit by a second winding on inductor 17, see FIG. 1, the
lamp will ionize and then the voltage will stabilize at the
operating arc voltage of the particular lamp used. The tank circuit
via transistor 11 will accept exactly the energy each cycle that
the lamp removes for operation. Further, since heating energy is
only required for starting, we can see that starting to operate
cathode heater watts are about 4 to 1, and up to 9 to 1 (square of
starting and operating cathode heater voltage). This is a very
desirable characteristic since it conserves energy during
operation, thus providing the maximum possible lumens per input
watt.
Further, we should consider the fluorescent lamp characteristic. It
is such that the lumen efficiency is adversely affected by form
factors drastically different from a sine wave. (Peak to RMS
ratio). Because of the sinusoidal operation of the tank circuit we
deliver a very acceptable wave shape to the lamp. This further
improves lumen efficiency over other inverter ballast
approaches.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an improved combination
inverter circuit, resonant circuit and resonant current monitor for
operating the inverter.
Another object of the invention is to provide a combination
inverter circuit, resonant circuit, resonant current monitor and
means to connect the combination to a load and means to switch the
resonant current in the inverter circuit in synchronism with the
resonant current as the resonant current passes through zero.
Another object is to provide a solid state ballast which is simple
in construction, economical to manufacture and simple and efficient
to use.
Another object of the invention is to provide an improved solid
state ballast.
With the above and other objects in view, the present inventon
consists of the combination and arrangement of parts hereinafter
more fully described, illustrated in the accompanying drawing and
more particularly pointed out in the appended claims, it being
understood that changes may be made in the form, size, proportions
and minor details of construction without departing from the spirit
or sacrificing any of the advantages of the invention.
GENERAL DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic view of the one embodiment of the
invention.
FIG. 2 shows a schematic view of one of the transformers.
FIG. 3 shows a schematic view of the other transformer.
FIG. 4 is a schematic view of another embodiment of the
invention.
FIG. 5 shows a schematic view of another embodiment of the
invention.
FIG. 6 is a block diagram of the invention.
FIG. 7, curve A showing the wave shapes of the collector current
through the transistor 11 and curve B showing the collector-emitter
voltage of transister 11.
FIG. 8, curve A, is a curve showing the resonant current in
transistor 11 and curve B is showing the collector-emitter voltage
of transistor 11.
FIG. 9, curve A, is a curve showing the collector-emitter current
in the transistor 12, curve B is a curve showing the
collector-emitter voltage in transistor 12.
FIG. 10, curve A, is a curve showing the resonant current of
transistor 12 and curve B is a curve showing the collector-emitter
voltage of transistor 12.
DETAILED DESCRIPTION OF THE DRAWING
The purpose of this invention is to provide an efficient inverter
ballast circuit for powering a fluorescent lamp from a standard
sinusoidal line voltage source. The inverter ballast will operate
at a high frequency, above the human audible range; which
eliminates the problem of noise, increases the efficiency of lamp
operation, and decreases component size and subsequent cost and
switches the transistors which control the current in the resonant
circuit as the current in the resonant circuit passes through zero
and in synchronism with the transistors.
The Resonant Oscillator
The oscillator used to generate a high frequency voltage for
driving the fluorescent lamp 55 is a two transistor resonance
maintenance circuit connected to a series resonant circuit. The
entire circuit is made up of five elements, (1) a source of
electricity, (2) a series resonant circuit designed to resonate at
a predetermined frequency, (3) a switching means connecting the
resonant circuit to the source of electricity, (4) a resonant
current monitor means for actuating the switching means, and
(5)means for connecting a load to the resonant circuit.
Since it is the current flowing in the resonant circuit that
commands the transistor to switch, it is axiomatic that the command
will be in synchronism with that current and irrespective of the
values of the inductance and capacitance (within wide frequency
limits) the circuit will always operate at resonance. The
transistors will switch in synchronism with that resonant
current.
The only limitation on zero switching is not in the circuit itself,
but may result from limitations in the transistors themselves in
the form of a delay in transistor switching due to electrical
charges stored in the transistor and to a very minor degree
limitations in the current transformer. With high quality
transistors and high quality current transformers, the transistors
would switch exactly at zero irrespective of the values of the
inductor and the capacitor within design limits. Applicant's test
shown in the sketches reproduced in the drawings and supported by
the attached Affidavit, show that even with commercially available
components, the transistors switch at zero insofar as can be
determined from ordinary laboratory equipment. Applicant has
attempted to claim this zero switching as occurring "as the
resonant current passes through zero". This is intended to cover
variations from zero that may occur with commercially available
components which is indistinguishable in the test Applicant has
made.
The source of electricity may be any suitable source of direct
current and it can be 120 volt AC circuit connected to the
switching means through a full wave rectifier as shown or any other
suitable source of direct current.
The switching means may be any suitable electronic valve such as a
transistor with a control element connected to the resonant current
monitor. The capacitor C22 may have a value of 0.081 microfarads
and the inductance may have a value of 4.7 millihenries. The
transformer 13 may be a suitable ferrite core transformer. The
transformer 13 has a core magnetically connecting to the primary
winding 18 and to the secondary windings 19, 20 and 21. The current
transformer has a suitable ferrite core which may be in the form of
a ring on which the windings are wound as shown.
When power is applied to the input terminals, 66 and 68 of the
full-wave rectifier 27, the input voltage is filtered by the
capacitor 21, this DC voltage is applied to the network which
includes transistors 11 and 12, causing transistor 11 to turn on.
This causes capacitor 22 to start charging through primary winding
14 and primary winding 18. The primary winding 18 of the high
leakage reactance transformer 17 is magnetically coupled to
secondary windings 19, 20 and 21. Secondary winding 20 is used to
drive the fluorescent lamp 55 which is of the ionizable gas type
lamp.
The transformer 13 is a current transformer used to sense current
flow in the resonant loop made up of primary winding 14 and primary
winding 18 and condensor 22 and to synchronize the switching of
transistors 11 and 12 with the resonant current. A current
transformer as used herein is one having a primary winding
connected in series with a circuit carrying a current and the said
primary winding carrying said current wherein the primary winding
is a few turns, that is a small number of turns. When current is
flowing into the terminal 44 (dots on the drawing indicate instant
polarity at a given time) current is flowing out of terminal 40
because the windings of transformer 13 are magnetically coupled.
This turns transistor 11 on and turns transistor 12 off. When
condensor 22 becomes fully charged, current flow passes through
zero and reverses in the resonant loop. This reversal of current is
sensed by the current transformer 13 which turns off transistor 11
and turns transistor 12 on. Capacitor 22, through resonant action
will transfer its charge to the opposite polarity, again causing
current to pass through zero and reverse in the capacitor 22 loop.
This second reversal is sensed by transformer 13 which turns
transistor 11 on and turns transistor 12 off. With commercial
tolerance components the switching may occur slightly off the zero
current point but with precise tolerance components the switching
will be exactly at zero. The phrase "when passing through zero" is
intended to mean switching at essentially zero which was, in tests
made on the circuits tested by Applicant, as closely as can be
determined from the photographs from which FIGS. 7 through 10 were
taken.
Transistors 11 and 12 are now maintaining resonance in the
capacitor 22 loop. This oscillating current and the subsequent
voltage generated by this charging and discharging of capacitor 22
generates a voltage in primary winding 18. This voltage can be
either stepped up or down, to meet the requirements of any size
fluorescent lamp connected to the output of secondary winding
20.
The resonant frequency of the oscillator is set by the size of
capacitor 22 and the inductance of primary winding 18. The ratio of
turns of primary winding 18 to secondary winding 20 is utilized to
reflect the fluorescent lamp load impedance into the primary
circuit in order to dampen the primary circuit.
The Lamp Output
Prior to lamp ionization, current is applied to the cathodes of the
windings 19 and 21 for heating purposes. This feature improves lamp
life for virtually no cost. During this mode the lamp is in a high
impedance state, the high impedance allows the secondary winding 20
voltage to be high. Because the voltage of winding 20 is high, the
voltage of winding 19 and the voltage of winding 21 are high enough
to generate substantial heating current in the lamp filaments. When
the lamp 55 becomes ionized or turns on, its impedance becomes low.
This low impedance reflected into the resonant loop (damping)
forces the secondary voltage to a low value, which in turn forces
the voltage on heaters 56 and 61 to a negligible value because of
the turns ratio of windings 19 and 21 to the winding 20. The
fluorescent lamp 55 is now on with negligible filament heating
current flowing. FIGS. 7, 8, 9 and 10 show voltage and current
readings taken during the operation of a circuit like the one shown
in FIG. 1 of this application. A first sensor was connected to the
circuit for measuring current of the collector of transistor 11,
another sensor for measuring the current of the collector of
transistor 12, a third sensor for measuring the current in the
resonant circuit, a fourth sensor for measurement of voltage across
transistor 11, a fifth sensor for measuring the voltage across
transistor 12. The circuit was operated with the sensors connected
to a cathode ray oscilloscope. FIG. 7, curve A shows the wave shape
shown by the oscilloscope of the collector current through the
transistor 11, curve B, the collector-emitter voltage of transistor
11. FIG. 8, curve A, is a curve showing the resonant current in
transistor 11 and curve B is a curve showing the collector-emitter
voltage of transistor 11. FIG. 9, curve A is a curve showing the
collector-emitter curve current in transistor 12, curve B is a
curve showing the collector-emitter voltage in transistor 12. FIG.
10, curve A is a curve showing the resonant current of transistor
12 and curve B is a curve showing the collector-emitter voltage of
transmitter 12. In the curves, the vertical axis of the curves
shows that the transistors switch when the resonant current (upper
curve in all pictures) passes through 0.
In the embodiment of the invention shown in FIG. 4, an inverter
ballast circuit utilizing the basic principles set forth in the
embodiment of the invention in FIG. 1 is shown.
The oscillator used to generate the high frequency voltage for
driving a fluorescent lamp 55 includes the two transistor resonance
maintenance circuit. When power is applied to the input terminals
166 and 168, input voltage is divided by capacitor 133 and
capacitor 133'. Secondary winding 120 on transformer 117 is
connected to the fluorescent lamp 155. The resonant loop is made up
of the primary winding 114 on the current transformer 113 and the
primary winding 118 on the high leakage reactance transformer 117
and the capacitor 122. The DC voltage is applied to the network
which includes transistors 111 and 112 causing transistor 111 to
turn on. This causes the capacitor 122 to start charging through
the primary windings 114 and 118. Primary winding 118 of the high
leakage reactance transformer 117 is magnetically coupled to the
secondary winding 120. Secondary winding 120 is used to drive the
fluorescent lamp 155 which is of the ionizable gas lamp type.
The transformer 113 is a current transformer used to sense current
flow in the resonant loop and to synchronize the switching of the
transistors 111 and 112. When current is flowing in the terminal
144 (dots on the drawing indicate instant polarity at a given
time), current is flowing out of terminal 140 because the windings
of transformer 113 are magnetically coupled. This turns the
transistor 111 on and turns transistor 112 off. When condensor 122
becomes charged, current passes through zero and reverses in the
condensor 122 loop. This reversal of current is sensed by the
current transformer 113 which turns off transistor 111 and turns
transistor 112 on. Capacitor 122, through resonant action, will
transfer its charge to the opposite polarity, again causing current
to pass through zero and reverse in the capacitor 122 loop. The
second reversal is sensed by transformer 113 which turns transistor
111 on and turns transistor 112 off. Transistors 111 and 112 are
now switching in synchronism with the resonant current as shown by
FIG. 8 and FIG. 10 maintaining resonance in capacitor 122 loop.
This oscillating current and the subsequent voltage generated by
this charging and discharging of capacitor 122 generates a voltage
in primary winding 118. This voltage can be either stepped up or
stepped down to meet the requirements of any size fluorescent lamp
connected to the output of secondary winding 120.
The resonant frequency of the oscillator is set by the size of the
capacitor 122 and the inductance of primary windings 114 and 118 to
reflect the fluorescent lamp load impedance into the primary
circuit in order to dampen the primary circuit.
The circuit of the embodiment of FIG. 4 has the beneficial effect
described in connection with the other embodiments of the
invention.
Now, with specific reference to the embodiment of the invention
shown in FIG. 5, an alternate embodiment of the invention is shown
wherein the resonant loop is indicated at 260 made up of the
primary winding 280 of transformer 282 and the secondary winding
220 of transformer 217. Current transformer 213 is connected in
series with primary 218 and to the line 241. Secondary winding 215
is connected to the base of the transistor 211 at 235 and the
terminal 243 is connected to the base 236 of the transistor 212.
The terminal 242 is connected to the line 233. The input to this
circuit may be considered to be lines 232 and 233. Filter capacitor
221 is connected across the output of a full wave rectifier as in
the other embodiments.
The corresponding parts of the embodiment in FIG. 5 have numbers
similar to the corresponding parts on the other embodiments of the
invention, and it will be seen that the oscillator used generates a
high frequency voltage for driving the fluorescent lamp 255. When
the power is applied to input terminals 232 and 233 out of the full
wave rectifier, the input voltage is filtered by capacitor 221 and
this voltage is applied to the network which includes transistor
211 and 212 causing transistor 211 to turn on. This starts current
flowing in the loop which includes primary windings 214 and 218
which induces a voltage in the winding 220 which in turn starts a
current flowing in the loop 260 and condensor 222 starts charging.
Transformer 213 is used to sense current flow in the loop made up
of windings 214 and 218 to synchronize the switching of transistors
211 and 212. When current is flowing into the winding 214 (dots on
the drawing indicate instant polarity at a given time), current is
flowing out of terminal 240 because the windings of transformer 213
are magnetically coupled. This turns transistor 211 on and turns
transistor 212 off. When condensor 222 becomes fully charged,
current passes through zero and reverses in condensor 222 loop,
thus reversing the currents in the loop made up of windings 214 and
218. The reversal of current is sensed by the current transformer
213 which turns the transistor 211 off and turns transistor 212 on.
Capacitor 222, through resonant action will transfer its charge to
the opposite polarity again causing current to pass through zero
and reverse in the capacitor 222 loop and in the loop made up of
windings 214 and 218. The second reversal is sensed by transformer
213 which turns transistor 211 on and turns transistor 212 off.
Transistor 211 and 212 are now maintaining resonance in capacitor
222 loop. This oscillating current and subsequent load is generated
by this charging and discharging of capacitor 222 generating a
voltage in primary winding 218. This voltage can be either stepped
up or stepped down, depending on the requirements of the
fluorescent light. The resonant frequency is set by capacitor 222
and inductance of primary windings 280 and the leakage inductance
of secondary 220. The operation of this circuit will be generally
like that in the circuit shown in the other embodiments of the
invention; however, the resonant loop 260 is separate from the
current monitoring loop 261.
FIG. 4 demonstrates a circuit where substantially equal energy is
introduced into the circuit during each half cycle. This is
accomplished by means of capacitors 133 and 133'. A similar effect
may be accomplished by substituting a second source of energy for
capacitor 133'.
The circuit described herein is illustrated using a fluorescent
lamp application for example. There are many other examples where
generating an unlimited ouput voltage could be utilized. Different
types of high voltage lamp applications, ignition systems, and
ignitors for rocket engines are other examples of the many which
are only limited by the imagination of the designer.
With regard to the block diagram shown in FIG. 6, the numbers on
the blocks correspond to the numbers shown in the embodiment of
FIG. 1. In FIG. 6, load means 55 is shown connected to a load
coupling means 20 which is magnetically coupled to the first
magnetic means 18 which in turn is driven by the resonant capacity
of means 22. Current monitoring means 14 is connected to the
switching means 11 and 12 which in turn are connected to the DC
source 27 which is supplied through the line 25.
The foregoing specification sets forth the invention in its
preferred, practical forms but the structure shown is capable of
modification within a range of equivalents without departing from
the invention which is to be understood is broadly novel as is
commensurate with the appended claims.
* * * * *